No-one is quite sure why, although some researchers have suggested that it may be added to boost the effect of cocaine in the brain.
Now a brief article in the Journal of Analytical Toxicology suggests this may indeed be the case based on the neurological effects of the two substances.
Street drugs are typically ‘cut’ with additional substances, often to bulk them out, but occasionally to alter the effect of the main substance. As we discussed in a post on adulterants in heroin, this can be a way of changing the drug to give it a different effect to benefit the dealer.
As an excellent article on Erowid notes, the fact that cocaine is cut with only small amounts of levamisole (only 6% of the deal in one study) suggests that it is not being used just as a handy powder to thin out the coke – more likely, it is being added for a specific effect.
Levamisole is, in some respects, similar to nicotine and the drug binds to specific nicotine-triggered receptors for the neurotransmitter acetylcholine and causes the nerve cell to respond. It turns out that this is most likely to increase activity in the body’s ‘fight-or-flight’ system – the sympathetic nervous system.
In fact, this is exactly how the drug has its deworming effect. In worms, it targets nerve cells involved in muscle activity, causing the muscles to contract. The worm is paralysed and so can be easily expelled from the body.
As cocaine also stimulates the body, the two drugs could combine to cause additional arousal.
This effect would largely be on the peripheral nervous system, outside the brain, but levamisole might also boost the effect of cocaine directly within the brain – enhancing pleasurable feelings.
In the brain, levamisole likely also enhances the release of glutamate, a neurotransmitter that is known to encourage or excite the function of neurons.
We known cocaine boosts dopamine function in the reward system, but the reward system is not single brain area. It’s actually a network of related structures deep within the brain that have connections that communicate and feedback their activity levels to carefully tune their running. An essential part of the feedback mechanism uses glutamate.
To use a sound system analogy, if cocaine cranks up the volume by boosting dopamine, levamisole might work by increasing power to the speakers by upping glutamate levels. The effects add up and the high is amplified.
What this means is that dealers can sell less actual cocaine but users get a similar effect from the smaller amount.
However, this comes at a price. The additional ramping up of the ‘fight-or-flight’ system is likely to put an additional strain on the heart and heart failure is one of the most common cocaine-associated fatalities.
Levamisole also causes the immune system to stop working so well by killing off white blood cells (in fact, this is why it is rarely used in humans in modern medicine) and several cases of life-threatening illness caused by levamisole-cut cocaine have already been reported.
The fact that this additive has been appearing at all, is, in itself, quite surprising. The fact that this relatively obscure compound has become so common in the global cocaine industry might suggest that it was selected on the basis of its pharmacological properties.
In other words, on the basis of the study of neuroscience. One study reported that professional heroin cutters can charge up to $20,000 a kilo and I wouldn’t be surprised whether the big players in the cocaine industry can afford to pay for neuroscientists or pharmacologists to tweak their products.
Link to PubMed entry for brief article on possible effects of levamisole.
Link to excellent Erowid reviewing findings on levamisole-cut cocaine.
Link to Wall Street Journal on prevalence of levamisole in US cocaine.