29 CFR Part 1630, Regulations to Implement the Equal Employment Provisions of the ADA (Title I Regulations with amendments issued through May 2016)

(4) Condition, manner, or duration—

(i) At all times taking into account the principles in paragraphs (j)(1)(i) through (ix) of this section, in determining whether an individual is substantially limited in a major life activity, it may be useful in appropriate cases to consider, as compared to most people in the general population, the condition under which the individual performs the major life activity; the manner in which the individual performs the major life activity; and/or the duration of time it takes the individual to perform the major life activity, or for which the individual can perform the major life activity.

(ii) Consideration of facts such as condition, manner, or duration may include, among other things, consideration of the difficulty, effort, or time required to perform a major life activity; pain experienced when performing a major life activity; the length of time a major life activity can be performed; and/or the way an impairment affects the operation of a major bodily function. In addition, the non-ameliorative effects of mitigating measures, such as negative side effects of medication or burdens associated with following a particular treatment regimen, may be considered when determining whether an individual's impairment substantially limits a major life activity.

(iii) In determining whether an individual has a disability under the “actual disability” or “record of” prongs of the definition of disability, the focus is on how a major life activity is substantially limited, and not on what outcomes an individual can achieve. For example, someone with a learning disability may achieve a high level of academic success, but may nevertheless be substantially limited in the major life activity of learning because of the additional time or effort he or she must spend to read, write, or learn compared to most people in the general population.

(iv) Given the rules of construction set forth in paragraphs (j)(1)(i) through (ix) of this section, it may often be unnecessary to conduct an analysis involving most or all of these types of facts. This is particularly true with respect to impairments such as those described in paragraph (j)(3)(iii) of this section, which by their inherent nature should be easily found to impose a substantial limitation on a major life activity, and for which the individualized assessment should be particularly simple and straightforward.