Although I wouldn't call these rules complicated, they are extremely detailed. CRA also closely monitors these claims and challenges them frequently. Unfortunately, they often apply to low-income taxpayers without the means to hire professionals to deal with their affairs.
The upside (if there is such a thing when dealing with medical problems) is that the claims can save thousands in income tax. If you or anyone in your family is incurring substantial medical costs, make an appointment with your accountant to review the situation. This should be done prior to income tax time - don't wait until March or April!
Consider the following:
The above list is not intended to be exhaustive but may give some ideas for income tax medical claims.