Original sentence: As with other amphetamines, tolerance to methamphetamine is not completely understood but is known to be sufficiently complex that it cannot be explained by any single mechanism.It is highly dependent on dosage, duration of use, and frequency of administration.Prolonged overstimulation of dopamine receptors caused by methamphetamine may eventually cause the receptors to downregulate in order to compensate for increased levels of dopamine within the synaptic cleft.Short-term tolerance can be caused by depleted levels of neurotransmitters within the synaptic vesicles available for release into the synaptic cleft following subsequent reuse (tachyphylaxis).Short-term tolerance typically lasts until neurotransmitter levels are fully replenished; because of the toxic effects on dopaminergic neurons, this can be greater than 2–3 days.The extent of tolerance and the rate at which it develops vary widely between individuals, and even within one person.To compensate, larger quantities of the drug are needed in order to achieve the same level of effects.Tolerance to the awakening effect of amphetamines does not readily develop, making them suitable for the treatment of narcolepsy