Does tolerance (tachyphylaxis) occur with long-term use of tadalafil?

No, there have been no reports or evidence  showing tachyphylaxis or tolerance with  long-term tadalafil therapy. Tachyphylaxis is  the rapid, progressive decrease in response to  a given dose following repetitive administration  of the drug. Tolerance is the reduction in  response to the drug after repeated administrations  over time, the result being that a higher  dose is required to produce the same effect that  Supplement  152 Vol. 2, No. 1, pp. 141–157, March 2005  was once obtained at a lower dose. In a clinical  study of patients using tadalafil 10 – 100 mg  daily for three weeks, [51] no patients withdrew  due to tachyphylaxis (perceived sudden lack of  efficacy). In another clinical study of patients  taking tadalafil on an ‘as needed’ (PRN) basis  for 6months, significant improvements in erectile  function were demonstrated on all efficacy  variables at both 3 and 6 months. In addition  the mean change from baseline of intercourse  success observed in the initial 3 months of  therapy were similar to that observed in the  final 3-month treatment period. The consistent  efficacy at these two time points suggests that  there is no tolerance to tadalafil over time.  Furthermore, the low rate of discontinuations  due to lack of efficacy in a long-term (18 to 24  months), open-label safety study provides  further support to that observation.