In the wake of news that Clifton Promise, Jock Paget’s Land Rover Burghley CCI**** winner, tested positive for reserpine as well as Kevin McNab’s Burghley ride Clifton Pinot, we did some research on the drug. Thanks to Chronicle medical editor Joe Davis, DVM, his research assistant Juliet Graham and Barbara Forney, VMD, for their help.

What is reserpine?
Reserpine is an indole alkaloid anti-hypertensive and anti-psychotic drug. It’s naturally occurring and is extracted from the root of Indian Snakeroot (Rauvolfia serpentina) or Poison Devil’s Pepper (Rauvolfia vomitoria) plants found in India and Africa. In traditional herbal medicine, the root was brewed as a tea and used in humans to treat hypertension, insanity, snakebite and cholera. The purified alkaloid, reserpine, was isolated in 1952 and is considered the first modern drug to treat hypertension.

What are the most common legitimate uses?
The most common legitimate use in horses is for long-term sedation for enforced rest when recovering from injury, and for this purpose it is very helpful. Reserpine binds to the storage vesicles of neurotransmitters, particularly norepinephrine, serotonin and dopamine. It takes many hours or days to reach full effect and continues to have some subtle sedating effects for many days after the last dose.

What are the most common illegitimate uses?
The most common illegitimate use was for making quieter show hunters, but once there was a test for it, it all went away.

How is it administered?
It can be given intramuscularly or orally. 

Is it in other medications or therapies or would it just be given on its own?
It is usually administered by itself.

How long is the recommended withdrawal period for reserpine before competing at a Fédération Equestre Internationale event?
Recommended FEI withdrawal is 90 days.

Does the withdrawal depend on the form administered?
That time frame does not depend on the route. 

Is there a threshold limit for reserpine, or is it no tolerance whatsoever?
FEI is going to be no tolerance. There isn’t any legitimate use in the competing sport horse. FEI withdrawals are usually quite conservative, so that suggests that three months is the outer limit of detection.

Are there ever false positives?
There can be false positives. Natural occurrence is a possibility since it has been isolated from Indian Snakeroot and may be present in other plants. The Greater Periwinkle, Vinca major, is a weed that grows in the United Kingdom in the summer, and it contains vincamine and reserpine. Some herbal products have also been implicated in positive tests for reserpine.

Are there short-term or long-term negative effects of reserpine?
The most common adverse effect is diarrhea, which we see regularly. It usually resolves with a lower dose of the drug. Different horses vary greatly in their sensitivity to the drug, and other side effects may include colic, sweating, depression, droopy eyes and a dropped penis.