M99: Veterinary Drug is a Killer in the Hands of Unscrupulous Individuals


What is M99 and why has it become so popular among rhino-slaughtering organized crime syndicates?

Across the African continent, a strictly regulated veterinary drug that has aided rhino conservation efforts for decades has now become the animals’ worst nightmare.

Rhino-slaughtering organized crime syndicates – typically involving ‘game industry insiders’ and their veterinarian accomplices – have taken a liking to M99, as it has increased the efficiency of their brutal, profit-seeking, criminal activities.

Although M99 can accomplish wonderful things when used as intended, the increasingly common misuse and abuse of the narcotic has taken the rhino crisis to new extremes – especially in South Africa.

What is M99?

Etorphine (commonly called ‘M99’) has been fundamental to the anesthesia of large game mammals in proper veterinarian-controlled settings.

First engineered in the ‘60s, it is a very powerful opioid that contains pain-relieving qualities said to be thousands of times more potent than that of morphine, a related substance.

The drug primarily impacts the neurological system and, though it does appear to have some slight narcotic effects on the animal’s cognizance, it is not considered a tranquilizer or a sedative.

As a result, it is most commonly used in conjunction with other drugs in order to achieve full anesthesia.

Although the animal may be sedated and unable to make voluntary physical movements during these events, it is not necessarily fully “unconscious”, as it may often be somewhat aware of its surroundings.

Why is this drug favored by wildlife professionals?

M99 is largely favored for large game animal captures and veterinary procedures because of its fast-acting properties and the fact that it can be used successfully in low doses.

As with any case of immobilization, the probability of injury and harmful physiological effects increases with the amount of time an animal spends ambulatory after being darted, or in an unbalanced state of intoxication following administration of the antidote.

Thus, the accelerated rate at which animals become disenabled when darted with M99, as well as the drug’s prompt response to the reversal, make it an extremely favorable drug for captures in wild or free-ranging situations – especially those involving rhinos.

If done correctly, they tend to succumb to the effects within a matter of moments.

Scientific literature has reported ranges of two to thirteen minutes, but averages seem to fall within about seven to eight minutes.

The rapid onset obviously limits the distance the animal is capable of moving after being darted, which in turn reduces its chance of suffering injury or becoming too worked up in a physical sense.

A 2007 article in the Journal of Zoo and Wildlife Medicine reports such distances ranging from around 500 to almost 1,270 meters were observed across a study that involved the anesthesia of some 31 white rhinos.

Additionally, much unlike a bullet, the trajectory and velocity of a dart (upon being fired) is heavily impacted by the volume of fluid it contains.

As M99 can be successfully administered in low doses, the darts contain a lesser volume of liquid, which helps to maintain better accuracy when the darter takes aim.

How do the experts use it?

When used alone, etorphine is known to have some potentially serious side effects for rhinos, such as hypertension, respiratory depression, decreased motility in the digestive tract, inhibited ventilation, tachycardia, brachycardia, abnormal blood pH levels, and hypoxemia (reduced amounts of oxygen in the blood).

In a normal, veterinarian-controlled setting, the experts counteract these factors by using a carefully calculated combination of drugs – typically a mix of M99, a sedative, other types of opioids, and often another medicine that hastens the rate at which the medications are absorbed by the animal’s body.

Working synergistically, these combinations aid in a smoother immobilization process, as well as a shortened time period between the dart hitting the animal and it becoming consequently incapacitated.

Under normal circumstances, the animals receive an antidote for the anesthesia after the given procedure has been completed and it soon recovers to its previous state.

Why and how do rhino horn syndicates use it?

Media often report that crime rings favor darting the animals because dart guns are much quieter than typical firearms, thus drawing less attention to their criminal acts.

However, it is more likely that these groups have resorted to using veterinary drugs – which they most often shoot from the cover of a helicopter – because this method allows them to acquire more horns in a shorter period of time.

As you can imagine, being able to quickly fly in and fly out of the crime scene also reduces their chances of being caught in the act or otherwise being tracked by anti-poaching units or private rhino owners.

The M99 will drop the animal rapidly, meaning they do not have to give chase.

If shooting a rhino with a bullet from any type of aircraft, a precise kill shot would be needed to prevent the animal escaping with only an injury.

This makes for a greater chance of losing the pachyderm in the bush and not being able to collect its horn.

To successfully make such a shot would be difficult for even a sharpshooter, as the areas in which a bullet could actually kill a rhino are few and very small in area — not to mention the instability created by the helicopter’s movements.

When using a drug-filled dart to shoot the creature, the target areas are much larger, providing a much greater chance for successfully delivering the narcotics.

In other words, a dart is easier and more likely to accomplish what is needed than a bullet.

In syndicates’ use of M99, it seems the rhinos are typically overdosed and left to a slow and painful death after the prized (but medicinally useless) horn has been removed.

The rhino may die of any number of related factors, including extreme blood loss from the horrific wounds, respiratory arrest, cardiac arrest, or any other number of drug-induced medical conditions.

How much of the drug is used for rhinos?

M99 is typically sold in 10.5 milliliter (ml) bottles at a concentration of 9.8 milligrams (mg) of etorphine per ml of fluid, which means there are about 102.9 mg of M99 per bottle.

A 2003 report in South African Medical Journal suggests that M99 is administered to rhinos in doses ranging from 0.5 – 10 mg.

It seems a range of three to five mg is most commonly observed in scientific literature from free-ranging field studies.

At these amounts, a single bottle of M99 could immobilize anywhere between 20-34 rhinos.

Yet, assuming that these syndicates are using larger doses than would normally be administered (say the aforementioned 10 mg) — in order to decrease the time it takes for the animal to reach recumbency and to ensure success in bringing the animal down — a single 10.5 ml vial of the drug may be used for as few as ten rhinos.

M99 is controlled by legislation

This substance is extremely dangerous for humans — even skin contact with a drop of M99 is said to be capable of killing a person.

As such, the narcotic is heavily regulated by legislation in most, if not all countries around the world.

Most of these regulations restrict the use of etorphine to qualified veterinarians only.

Typically, a meticulous record of each and every use of the drug must be kept in a logbook wherever the medicine is stored.

M99 is apparently considered a Schedule 7 narcotic and is governed by the nation’s Medicines and Related Substances Act.

Under Section 22C(c) of this law, it is explicitly stated that use of the narcotic is restricted only to qualified veterinarians and medical doctors.

“(5) No person shall compound or dispense a medicine unless he or she is authorised thereto in terms of the Pharmacy Act, 1974, is a veterinarian or is the holder of a license as contemplated in subsection 1(a).”

Policies set forth by the South African Veterinary Council further clarify the acceptable use and possession of the drug.

Veterinarians are to be the only end users of scheduled substances used for anaesthetising animals.

Scripts are not to be issued for use of these scheduled substances by clients.

Unfortunately, at least five South African veterinarians have been charged with contravening the Medicines and Related Substances Act in recent times, including Karel Toet, Manie du Plessis, Douw Grobler, Johannes Kruger, and Buti Chibase.

It is believed the charges laid against them are linked to rhino plundering crimes.


Brinks, C.F. and J. Erasmus, “An Unusual Case: Etorphine Poisoning,” South African Medical Journal 93(10): 761-762.

Immobilon (M99, Etorphine hydrochloride),” VetaPharma Ltd., accessed 28 February, 2012

Kock, Michael D., “Use of Hyaluronidase and Increased Etorphine (M99) Doses to Improve Induction Times and Reduce Capture-Related Stress in the Chemical Immobilization of the Free-Ranging Black Rhinoceros (Dicoeros bicornis) in Zimbabwe,” Journal of Zoo and Wildlife Medicine 23(2): 181-188.

Portas, TJ, “A review of drugs and techniques used for sedation and anaesthesia in captive rhinoceros species,” Australian Veterinary Journal 82(9): 542-549.

Wenger et al., “The Cardiopulmonary Effects of Etorphine, Azaperone, Detomidine, and Butorphanol in Field-Anesthetized White Rhinoceros (Ceratotherium simum),” Journal of Zoo and Wildlife Medicine 38(3): 380-387.

Sarah Pappin

I am a writer for Saving Rhinos, as well as for her sister blog, Project Pangolin. You may know me from my previous role at Bush Warriors. I am a biologist-turned-writer, with a BSc in wildlife science from Oregon State University. When I'm not blogging, I enjoy loud music, creating art, hula hooping, and being outdoors.

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