There are many factors that affect the time it takes for a drug to reach your bloodstream. Some drugs are more easily absorbed than others. The length of time a drug stays in your bloodstream depends on the drug and its family. Some drugs are broken down by the stomach and therefore may take longer to enter your bloodstream. Other drugs are metabolized in your liver and may stay in your bloodstream for a longer period of time.
Some drugs are absorbed into the body and then diffuse through the cell membrane. Drugs diffuse from a high concentration to a low concentration. The rate of diffusion is directly affected by the gradient in concentration. The size of the drug and its degree of ionization also contribute to the rate of drug diffusion. Small molecules tend to penetrate membranes more quickly. They also travel faster when the drug binds to small proteins.
The absorption curves of most drugs are very specific. The half-life is the time that a drug remains within your body. A drug’s half-life, or T1/2, refers to the time it takes to reduce its peak concentration by 50 percent. After approximately five half-lives, the drug is eliminated completely from the body. However, small quantities of a drug can stay in the bloodstream for longer periods of time, so your individual drug absorption curve may differ from one person to another.
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