Medical Allowance and Reimbursement
You can pay a component under medical allowance even on a monthly basis, but at the end of the year, the employee needs to submit bills to that extent (subject to the limits specified under Income Tax rules) so that it comes under medical reimbursement, which doesn't attract ESI and even Income Tax.
In case the employee is unable to submit the bills to that extent, then the total amount paid to him shall attract a deduction under Income Tax rules. The component should be named as medical reimbursement; failing which, it comes under regular wages and attracts both ESI and IT.
The employee even covered under ESI may not be able to go to the dispensary for petty illness and needs treatment, and to meet such expenses, this medical allowance will be used. Hence, this allowance is generally on a reimbursement basis.
To avoid all related issues, it is better to reimburse on submission of bills either quarterly, half-yearly, or annually so all the related issues can be avoided and it is helpful to the employee.