Why does the weight matter when consuming a certain amount of a specific drug?

Question

My question is actually referred to hallucinogenic substances, in particular to mushrooms. I can understand why alcohol or other substances that relate to body mass (fat in some cases) affect people to a greater or a lesser extent depending on their weight (for a given amount of a certain drug). What I do not understand (perhaps this is not even true) is why the more mass a person has, more grams of mushrooms that person has to take in order to get the same psychoactive effect. If the active substance finally goes to the brain, where is the weight's role in this process? People with experience in this recommends intakes of a certain amount of grams depending on one's weight. Does this have a logical reason?

Answer 1

It has a huge amount to do with metabolism - how quickly the body can burn through a certain chemical. It, also, has to do with how the medication will affect the individuals organs. Tylenol can cause the liver to "fail". The liver takes the tylenol and passes the left over into the blood, which is then filtered out by the kidneys. When too much tylenol is consumed, the liver is overloaded and overworked. A larger individual, or in this case an adult, would have more of a metabolic rate than a child would. This is due to the growth and development of the internal organs.

Answer 2

The explanation for mushrooms is really no different from that for alcohol. Neither of these drugs just simply enter the brain. There is a blood-brain-barrier that drugs and other substances has to cross. Also, there is disposition within other parts of the body. Not all of the drug goes to any one part. So, whether it's alcohol, hallucinogenic substances, or any other material, body mass will play a role in the dose. Another very important factor in drug dose is the liver enzymes that metabolize the drugs. There are high and low metabolizers in the population. Hope this helps answer your query.