38 CFR §17.3240

1. (a)
   1. (1)VA providers, or eligible entities and providers as defined in § 17.4005, will prescribe items and services in accordance with § 17.3230(a) and will do so in consultation with the veteran.
   2. (2)Once the item or service is prescribed under paragraph (a)(1) of this section, VA will either fill such prescriptions directly or will pay for such prescriptions to be furnished through a VA-authorized vendor.
   3. (3)The determination under paragraph (a)(2) of this section of whether a prescription will be filled by VA directly or will be furnished by a VA-authorized vendor will be based on, but not limited to, such factors as the veteran's clinical needs, VA capacity and availability, geographic availability, and cost.
2. (b)Except for emergency care under §§ 17.120 through 17.132, §§ 17.1000 through 17.1008, or § 17.4020(c), or urgent care under § 17.4600, prior authorization of items and services under § 17.3230 is required for VA to reimburse VA-authorized vendors for furnishing such items or services to veterans.