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**Table of Content**

Use the drug half life calculator to determine the amount of a drug still present in a patient’s body when half time and dosage are known.

The half life of a drug is the estimation of the time that the amount of a drug takes to be reduced by one-half. The symbol t1/2 is used for the half-life.Â

- Age
- Blood circulation
- Diet
- Excessive fluid
- Gender
- Kidney function
- Liver function
- Obesity
- Smoking

The formula that is used to find the half life of drug is as follows:

**\(\ Dosage(t) =\ Dosage(0)\times\ 0.5^{(\frac{t}{T})}\)**

**Where**

- T is the representative of the Half-life of a drug;
- t is the Time that has passed from the administration of the drug;
- Dosage(t) â€“ The drug amount present in a patient’s body
- Dosage(0) shows the drug quantity administered

Go through the steps outlined below:

- Measure the quantity of the drug dosage
- Determine the half-life timeÂ
- Put these values in the half-life formula as we have done in the following example.Â

Suppose you have the following values:

- Half Life Drug = 1 minute
- Dosage = 10 gÂ

Find the half life?

**Solution:**

Convert Grams to milligrams:

\(\ Dosage =\ 10\ \times\ 1000 =\ 10000\ mg\)

Put the given values in the half life drugs formula:

\(\ Dosage(t) =\ Dosage(0)\times\ 0.5^{(\frac{t}{T})}\)

\(\ Dosage(t) =\ 10000\ mg\times\ 0.5^{(\frac{1}{1})}\)

\(\ Dosage(t) = 5000\ mg\)

In the following table, we have mentioned some most commonly used substances and their half life.

Generic Name |
Brand Name Examples |
Half-life (T1/2*) |

Alprazolam | Xanax | 6-12 hours |

Amiodarone | Pacerone | 15-142 days |

Amphetamine | Adderall, Dexedrine | 10-12 hours |

Atenolol | Tenormin | 6-7 hours |

Clonazepam | Klonopin | 18-50 hours |

Cocaine | – | 50 minutes |

Diazepam | Valium | 20-100 hours |

Donepezil | Aricept | 70 hours |

Dutasteride | Avodart | 5 weeks |

Erenumab | Aimovig | 28 days |

Fluoxetine | Prozac | 2-4 days |

Lead | – | 28-36 days |

Mercury | – | 65 days |

Methamphetamine | Desoxyn | 6.4-15 hours |

Methylphenidate | Concerta, Ritalin | 2-3 hours |

Plutonium | – | 40 years (liver), 100 years (bone) |

Phenytoin | Dilantin, Phenytek | 7-42 hours |

Tetrahydrocannabinol (cannabis/marijuana) | – | Infrequent users: 1.3 days Regular users: 13 days |

No, The time that the drug takes to be eliminated from the body is the half life while the drug duration is the total time the drug remains inside the body.Â

A drug approximates takes 4 to 5 half lives to be eliminated from the body. When 4 to half-lives are passed the amount of the drug goes below the clinically relevant concentration and is normally considered eliminated. If you double the amount the elimination time also increases.Â

**References:**

goodrx.com: What does drug half-life mean?