Adults and children age 12 years and over
100–200 mg no more than every 3–4 hours. In timed-release form, the dose is 200–250 mg once a day. Timed-release forms should not be taken less than six hours before bedtime.
At recommended doses, caffeine can cause restlessness, irritability, nervousness, shakiness, headache, light-headedness, sleeplessness, nausea, vomiting, and upset stomach. At higher than recommended doses, caffeine can cause excitement, agitation, anxiety, confusion, a sensation of light flashing before the eyes, unusual sensitivity to touch, unusual sensitivity of other senses, ringing in the ears, frequent urination, muscle twitches or tremors, heart arrhythmias, rapid heartbeat, flushing, and convulsions.
Too much caffeine can cause anxiety, shaking, insomnia, and gastric and digestive disturbances. As dosage increases caffeine causes tachycardia (racing heartbeat), convulsions, coma, and death. Fatal dose is between 5 and 10 grams orally (14 Starbuck's 12 - ounce coffees at 375 mg caffeine each therefore constitute a potentially lethal dose of 5.625 grams caffeine), or 1 gram injected intracardially (directly into the heart à la Quentin Tarantino). Caffeine is physically addictive.
Precipitous reduction in or cessation of even low or moderate caffeine intake can, depending on individual susceptibility, result in withdrawal symptoms including anxiety, (sensation of) increased muscle tension, occasional tremor, weariness, weakness, fatigue, lethargy, apathy, drowsiness, headache including severe and/or debilitating headache, nausea, and vomiting.
Nicotine at 40- 60 mgm can be lethal. Nicotine aso accelerates the rate at which coffee is metabolized by the body.
What are the Effects of Nicotine?
Nicotine can do many things to the nervous system and not all of them are bad. Effects on the (+) side are things that are considered beneficial, while those on the (-) side are considered detrimental.
The positive effects are: anxiolysis (reduction of anxiety) ;cognitive enhancement, neuroprotection, analgesia; anti-psychotic vigilance; and cerebrovasodilation. The negative effects are GI distress, Hypertension, Hypothermia; Resp Distress and seizures.
This chart shows why several pharmaceutical companies (notably Abbott Labs, SIBIA, and Astra Arcus) are concentrating on nicotine research. You see, there are effects that people would like to replicate. So, the companies are working to design drugs which will mimic the good effects and avoid the bad ones.
One effect that is not listed on this chart is that nicotine can stimulate the division of SCLCs (small cell lung carcinomas), a cancer cell line, by several hundred percent. This fact is interesting because it may explain why certain types of lung cancer grow so rapidly in smoking patients.