OLYMPIA, Wash. (AP) — A new law compelling a $100 cap on insulin copayments in Washington is now in effect.

The law caps high deductible insurance insulin co-pays at $100 for a 30-day supply on plans issued or renewed after January 1st.

The law was approved by the Washington Legislature in March.

Studies show an estimated-one quarter of patients ration the medication because of cost or difficulty obtaining steady supplies.