It helps to be informed on your rights and best practices you can follow under such circumstances. Often, the firs question that comes an employees’ mind is:

Should I tell my Employer about my present medical condition?

Although it is not required to inform your employer or your medical condition at the time of interview or after, but it is good to inform your supervisor/boss on what could be expected further down the months with the particular medical condition you have.

You may request your boss not to disclose to other employees if you wish so, but always a good idea to keep your supervisor updated on any short-term or long-term sickness related absences. Not only that, your employers might also assist you to a better working schedule or surroundings making things easier for you.

Not telling your employer might not be the best idea in some circumstances – for instance what if your medication causes drowsiness for some time and you have to have it during work hours? Depending on your work environment it could be hazardous or just in appropriate. If your manager knows the reason of your inability to perform to your best during certain hours, it might well be excused.

You may also request flexible work schedule or part-time work when possible. In some countries legislation protects your right to work with long-term medical condition (cancer for example) you may also have the right to request flexible work schedule.

According to a 2002 National Health Interview Survey, arthritis is keeping almost 7 million American workers from performing their best at their workplace.

In an article on About.com, the authors discuss how to manage your work environment when dealing with arthritis. An article on arthritis-treatment-and-relief.com suggests the Ten Tips to Avoid Aches and Pains in the Office.

Family and Medical Leave Act

In the US you may take an extended medical leave to recover from your ailment. According to US Department of Labor, under the Family and Medical Leave Act (FMLA):

Covered employers must grant an eligible employee up to a total of 12 workweeks of unpaid leave during any 12-month period for one or more of the following reasons:

• for the birth and care of the newborn child of the employee;
• for placement with the employee of a son or daughter for adoption or foster care;
• to care for an immediate family member (spouse, child, or parent) with a serious health condition; or
• to take medical leave when the employee is unable to work because of a serious health condition.

Read more on this topic at the above DOL website link. Also note that there have been some changes in 2009 to this act, you must also get some related information from your employer on the possible leaves you can take.

There are limitations to coverage of FMLA (Source of this info: Findlaw):
The FMLA does not apply to all employers, or to all employees. The FMLA only covers employers with 50 or more workers, who have employed 50 or more workers for at least the past 20 weeks. It also applies to public agencies, regardless of the number of employees, and to elementary and secondary schools, both public and private. The FMLA only applies to employees who have worked for a covered employer for a minimum of 12 months, although these 12 months do not need to be consecutive. Additionally, the employee must have worked at least 1,250 hours for the employer during the previous 12 months, at a site where the employer has 50 or more employees within a 75-mile radius.

You might also want to know about the Disability Discrimination Act to understand your rights against discrimination at work due to any disability or medical condition.

The US Disability Discrimination Act

Title I of the Americans with Disabilities Act of 1990 prohibits private employers, state and local governments, employment agencies and labor unions from discriminating against qualified individuals with disabilities in job application procedures, hiring, firing, advancement, compensation, job training, and other terms, conditions, and privileges of employment. The ADA covers employers with 15 or more employees, including state and local governments. It also applies to employment agencies and to labor organizations. The ADA’s nondiscrimination standards also apply to federal sector employees under section 501 of the Rehabilitation Act, as amended, and its implementing rules.
(Get the complete information at: http://www.eeoc.gov/types/ada.html )