inhibitory effect of adenosine receptors on dopamine receptors, however the implications for humans are unknown. unlike most stimulants, caffeine has no addictive potential. caffeine does not appear to be a reinforcing stimulus, and some degree of aversion may actually occur, per a study on drug abuse liability published in an nida research monograph that described a group preferring placebo over caffeine. in large telephone surveys only 11% reported dependence symptoms. however, when people were tested in labs, only half of those who claim dependence actually experienced it, casting doubt on caffeine's ability to produce dependence and putting societal pressures in the spotlight. coffee consumption is associated with a lower overall risk of cancer. this is primarily due to a decrease in the risks of hepatocellular and endometrial cancer, but it may also have a modest effect on colorectal cancer. there does not appear to be a significant protective effect against other types of cancers, and heavy coffee consumption may increase the risk of bladder cancer. a protective effect of caffeine against alzheimer's disease is possible, but the evidence is inconclusive. moderate coffee consumption may decrease the risk of cardiovascular disease, and it may somewhat reduce the risk of type 2 diabetes. drinking 1-3 cups of coffee per day does not affect the risk of hypertension compared to drinking little or no coffee. however those who drink 2–4 cups per day may be at a slightly increased risk. caffeine increases intraocular pressure in those with glaucoma but does not appear to affect normal individuals. it may protect people from liver cirrhosis. there is no evidence that coffee stunts a child's growth. caffeine may increase the effectiveness of some medications including ones used to treat headaches. caffeine may lessen the severity of acute mountain sickness if taken a few hours prior to attaining a high altitude. ephedrine main article: ephedrine ephedrine is a sympathomimetic amine similar in molecular structure to the well-known drugs phenylpropanolamine and methamphetamine, as well as to the important neurotransmitter epinephrine (adrenaline). ephedrine is commonly used as a stimulant, appetite suppressant, concentration aid, and decongestant, and to treat hypotension associated with anaesthesia. in chemical terms, it is an alkaloid with a phenethylamine skeleton found in various plants in the genus ephedra (family ephedraceae). it works mainly by increasing the activity of norepinephrine (noradrenaline) on adrenergic receptors. it is most usually marketed as the hydrochloride or sulfate salt. the herb má huáng (ephedra sinica), used in traditional chinese medicine (tcm), contains ephedrine and pseudoephedrine as its principal active constituents. the same may be true of other herbal products containing extracts from other ephedra species. mdma tablets containing mdma main article: mdma