In this elementally open system the steady state of B always equal to R/q. The above scheme is only the necessary condition for the rate sensitivity phenomenon, and other pathways of deactivation of B may be considered, with the subsequent return to the inactive form of the receptor/enzyme A. Examples offer particular use of such (mathematical) models in endocrinology, physiology and pharmacology. Examples
Psychedelics
Psychedelics such as LSD-25 and psilocybin-containing mushrooms demonstrate very rapid tachyphylaxis. Opioids
In a patient fully withdrawn from opioids, going back to an intermittent schedule or maintenance dosing protocol, a fraction of the old tolerance level will rapidly develop, usually starting two days after therapy is resumed and, in general, leveling off after day 7. Whether this is caused directly by opioid receptors modified in the past or affecting a change in some metabolic set-point is unclear. Increasing the dose will usually restore efficacy; relatively rapid opioid rotation may also be of use if the increase in tolerance continues. Beta-2 agonists
Inhalation of an agonist for the beta-2 adrenergic receptor, such as salbutamol (albuterol in the US), is the most common treatment for asthma. Polymorphisms of the beta-2 receptor play a role in tachyphylaxis. Expression of the Gly-16 allele (glycine at position 16) results in greater receptor downregulation by endogenous catecholamines at baseline compared to Arg-16. This results in a greater single-use bronchodilator response in individuals homozygous for Arg-16 compared to Gly-16 homozygotes. However, with regular beta-2 agonist use, asthmatic Arg-16 individuals experience a significant decline in bronchodilator response.
More complete is an open system, namely, in its simplest form,

  
    
      
        R
        
          
            →
            
          
        
        A
        
          
            →
            
               
               
              p
              (
              S
              )
               
               
            
          
        
        B
        
          
            →
            
               
               
              q
               
               
            
          
        
        ,
      
    
    {\displaystyle R{\xrightarrow {}}A{\xrightarrow {\ \ p(S)\ \ }}B{\xrightarrow {\ \ q\ \ }},}
  
where R stands for the rate of production of A, p(S) is the activation rate coefficient explicitly expressing its dependence on the stimulus intensity S and q represents the rate coefficient of removal from the state B.