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Interaction: Does cannabis/THC interact with other drugs used for the treatment of diseases?

Leo Hollister

Although medical marijuana is not officially approved, marijuana has been tried empirically for treating a variety of medical disorders, such as nausea and vomiting associated with cancer chemotherapy, weight loss associated with AIDS, and spasticity from neurological diseases. In each instance, other drugs are also present. So far, no adverse interactions from such use have been reported. However, this might not reflect the true frequency. Unless one looks for something, one is not likely to find it. (...) The published literature, at least in regard to studies with humans, has been rather silent. Usually this silence indicates that no meaningful interactions have been observed in the real life use of marijuana as compared with experimental studies. (...) One of the most reasonable therapeutic uses of marijuana and THC has been to ameliorate the nausea and vomiting associated with cancer chemotherapy. Thus, cannabinoids will be used simultaneously with many highly toxic cancer drugs. (…) In none of the reports of use of THC or marihuana in patients simultaneously undergoing cancer chemotherapy has there been any mention of increased toxicity of anticancer drugs. Nonetheless, the absence of such reports may signify that no attempt was made to look for them. This avenue of research should be encouraged. A somewhat similar situation applies to the therapeutic use of orally administered THC in treating the weight loss associated with AIDS. (…) THC or marihuana has been used for treating spasticity associated with neurological disorders, such as multiple sclerosis and spinal cord injury. Since THC may be added to therapies with muscle relaxants, it would be of some interest to know whether such combined uses might be harmful. In one animal study in which THC was given with muscle relaxants, it was found to increase the desired effect of the latter drugs. In this case, the interaction might be advantageous.
(Please note: This text has been taken from a scientific article. Some sentences have been changed to improve understandability.)"
Modified according to: Hollister LE. Interactions of marihuana and D9-THC with other drugs. In: Nahas G, Sutin KM, Harvey DJ, Agurell S, eds. Marihuana and medicine. Totowa, NJ: Humana Press, 1999, pp. 273-277.

Franjo Grotenhermen

Cannabis and dronabinol (THC) have been used in combination with a multitude of medications without significant deleterious drug interactions. Clinical studies in the beginning of the 20th century often demonstrated mutual enhancement of therapeutic effects of cannabis preparations and other drugs. In modern therapeutic concepts a combination of cannabis/THC with other medications could also be of benefit for many indications. Cannabis has been used illegally by individuals suffering from many diseases concomitantly with numerous prescription medicines. No unwanted side effects of clinical relevance have been observed to date. (…) Other medicines may enhance or attenuate certain actions of cannabis/THC or certain actions of these medicines may be enhanced or attenuated by cannabis/THC. Moreover, it is possible that certain effects are enhanced and others reduced, as is the case with phenothiazines applied against side effects of cancer chemotherapy (see below). Of greatest clinical relevance is reinforcement of the sedating effect of other psychotropic substances (alcohol, benzodiazepines), and the interaction with substances that act on the heart (amphetamines, adrenaline, atropine, beta-blockers, diuretics, tricyclic antidepressants, etc.). (…)
· Anti-cholinergics: Atropine and scopolamine may increase the acceleration of heart frequency by THC.
· Anti-cholinesterases: Physostigmine antagonizes the psychotropic effects and the acceleration of heart frequency produced by THC. (…) · Anti-depressants (selective serotonin reuptake inhibitors): THC may increase the effect of fluoxetine.
· Anti-depressants (tricyclics): Frequency of the heart, blood pressure lowering and sedating effects of amitriptyline may be enhanced.
· Benzodiazepines: Respiratory depression and depression of the brain function may be increased. The antiepiletic action may be enhanced.
· Beta-blockers: They reduce increase of heart frequency associated with THC.
· Glaucoma: Several drugs that decrease intraocular pressure and cannabinoids may act additively.
· Neuroleptics: THC may antagonize the antipsychotic actions of neuroleptics. It may improve their therapeutic effects in motor disorders.
· Non steroidal antiinflammatory drugs (NSAID): Indomethacin, acetylsalicylic acid (aspirin), and other NSAIDs antagonize THC effects. Indomethacin significantly reduced subjective "high" and acceleration of heart frequency.
· Opiates: Enhancement of sedation and pain reduction.
· Phenothiazines: Prochlorperazine and other phenothiazines attenuate the psychotropic effects of THC and increase its antiemetic effects.
· Sympathomimetics: Amphetamines and other sympathomimetics enhance the acceleration of heart frequency and the increase of blood pressure.
· Theophylline: The metabolism of theophylline is accelerated by THC. Thus, higher doses of theophylline might be necessary.
(Please note: This text has been taken from a scientific article. Some sentences have been changed to improve understandability.)
Grotenhermen F. Practical hints. In: Grotenhermen F, Russo E, eds. Cannabis and cannabinoids. Pharmacology, toxicology, and therapeutic potential. Haworth Press, Binghamton/New York 2001, in press.

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