There is no universal winner — it depends on your specific drugs, your plan, and where you are in your Part D benefit year. Medicare Part D is usually best for expensive specialty medications and when you’re close to the $2,000 out-of-pocket cap. GoodRx or Cost Plus Drugs can be cheaper for common generics, drugs not on your formulary, or purchases early in the year before your deductible is met.
In this article
Medicare Part D
Insurance-based coverage with tiered copays. Counts toward your $2,000 out-of-pocket cap. Requires enrollment in a plan.
GoodRx
Free discount card usable at most retail pharmacies. No enrollment required. Does NOT count toward Medicare out-of-pocket spending.
Cost Plus Drugs
Cash-pay online pharmacy. Generic drugs at cost + 15% + $3 dispensing fee. Ships by mail. Cannot be combined with Medicare.
The Three Options Explained
Medicare Part D
Medicare Part D is prescription drug insurance. You pay a monthly premium, and in exchange your plan covers drugs on its formulary at negotiated rates. You pay copays or coinsurance based on the drug’s tier. Under the 2026 Part D structure, once you’ve spent $2,000 out-of-pocket in a calendar year, you pay $0 for all covered drugs for the rest of the year.
The major advantage of Part D is the accumulation toward the out-of-pocket cap. Every covered purchase moves you closer to $0 cost for the year. For expensive medications, this is the most powerful financial protection available.
GoodRx
GoodRx is a free drug discount program. You show a GoodRx coupon (on your phone or a card) at a participating pharmacy, and the pharmacy charges the negotiated GoodRx price instead of the retail price. There’s no membership fee and no enrollment — anyone can use it.
GoodRx negotiates group discount rates with pharmacy benefit managers and passes those savings to consumers. It is particularly strong for common generics, where it can beat Medicare copays substantially.
Mark Cuban’s Cost Plus Drugs
Cost Plus Drugs (costplusdrugs.com) is a direct-to-consumer online pharmacy that sells generic drugs at an extremely transparent price: manufacturer’s cost + 15% markup + $3 dispensing fee + $5 shipping. Because it operates outside the traditional pharmacy benefit manager (PBM) system, it cuts out significant middleman costs.
Cost Plus Drugs currently offers over 2,500 generic medications. It does not carry brand-name drugs, biologics, or controlled substances. It ships by mail only — no walk-in locations.
Real Price Comparison: 10 Common Senior Medications
The following prices are representative estimates based on typical Part D copays, published GoodRx prices, and Cost Plus Drugs published pricing. Your actual costs will vary by plan, pharmacy, location, and plan tier placement. Always check current pricing before making decisions.
| Drug (30-day supply) | Medicare Part D (est.) | GoodRx (est.) | Cost Plus Drugs (est.) | Best Option |
|---|---|---|---|---|
| Metformin 500mg (diabetes) | $0–$5 (Tier 1) | $4–$8 | $3–$6 | Medicare or Cost Plus |
| Atorvastatin 20mg (cholesterol) | $0–$5 (Tier 1) | $6–$12 | $4–$7 | Medicare |
| Lisinopril 10mg (blood pressure) | $0–$5 (Tier 1) | $5–$10 | $3–$5 | Medicare or Cost Plus |
| Amlodipine 5mg (blood pressure) | $0–$5 (Tier 1) | $7–$12 | $3–$5 | Medicare |
| Eliquis 5mg (blood thinner) | $40–$100 (Tier 3) | $450–$550 | Not available (brand) | Medicare (by far) |
| Ozempic 1mg (diabetes) | $40–$150 (Tier 3–4) | $800–$950 | Not available (brand) | Medicare (by far) |
| Omeprazole 20mg (acid reflux) | $0–$8 (Tier 1) | $6–$14 | $3–$5 | Cost Plus or Medicare |
| Gabapentin 300mg (nerve pain) | $0–$10 (Tier 1) | $10–$18 | $4–$7 | Medicare |
| Sertraline 50mg (depression) | $0–$5 (Tier 1) | $10–$16 | $4–$6 | Medicare or Cost Plus |
| Tamsulosin 0.4mg (prostate) | $0–$8 (Tier 1) | $12–$20 | $4–$6 | Medicare or Cost Plus |
The pattern is clear: for generic drugs, all three options are competitive and sometimes Cost Plus Drugs wins on price. For brand-name drugs, Medicare Part D is dramatically cheaper than GoodRx or paying cash, because GoodRx and Cost Plus Drugs do not have access to the negotiated rebate pricing that Part D plans receive from manufacturers.
The GoodRx + Medicare Rule You Must Know
This is the most important rule in this entire article, and it catches many seniors by surprise:
If you use a GoodRx coupon for a drug that IS covered by your Part D plan, that purchase does NOT count toward your Part D deductible or out-of-pocket cap. It’s as if you made the purchase outside of Medicare entirely.
Why does this matter so much? Because of the $2,000 out-of-pocket cap. If you’re on a specialty medication that costs $500/month in Part D copays, you’ll hit your $2,000 cap by April and pay $0 for the rest of the year. If you use GoodRx for three of those months instead — even if it saves you $50 per month — you delay reaching the cap and may end up paying more overall.
When GoodRx Beats Medicare
Despite the cap trap above, there are real situations where GoodRx makes more sense:
- Your drug is not on your plan’s formulary. If Medicare won’t cover your drug at all, GoodRx gives you a discounted cash price. This is often a substantial saving versus retail.
- Your plan placed the drug on a very high tier. If your plan assigned a generic to Tier 4 instead of Tier 1, GoodRx may be cheaper than your copay for that specific drug.
- Early in the year for a low-cost generic. If you haven’t met your deductible and your generic costs $8 at GoodRx but $590 worth of deductible needs to be burned first, GoodRx may make sense — depending on your other medications.
- You have a drug you take occasionally and won’t hit the cap. For someone who takes no specialty drugs and expects to spend well under $2,000 on drugs annually, the out-of-pocket cap is less relevant and GoodRx may simply be cheaper on a per-fill basis.
When Cost Plus Drugs Beats Both
Cost Plus Drugs shines in a narrow but meaningful set of scenarios:
- Generic drugs where your Part D plan’s Tier 1 copay is still higher than Cost Plus pricing. Some plans charge $5–$15 for Tier 1 generics; Cost Plus often comes in at $3–$7 for the same drug.
- Drugs not covered by Medicare that have a generic available. For drugs outside the formulary, Cost Plus transparent pricing is often lower than GoodRx.
- You don’t have Part D coverage at all. If you declined Part D at 65 (and are aware of the potential late enrollment penalty), Cost Plus offers a reliable, cheap source for generics.
The main limitations: Cost Plus ships by mail only (allow 3–5 business days), doesn’t carry brand-name drugs or controlled substances, and cannot be combined with any insurance including Medicare.
When Medicare Part D Is Clearly the Best Choice
- Any brand-name drug. GoodRx and Cost Plus Drugs charge retail-adjacent prices for brand-name drugs. Medicare Part D’s negotiated formulary pricing is almost always dramatically lower.
- Any specialty drug (biologics, cancer treatments, MS medications). Specialty drugs can cost $5,000–$30,000 per month at retail. Your Part D copay of $500–$1,000 is still enormous savings, and every dollar counts toward the $2,000 cap.
- When you’re likely to hit or have already hit the $2,000 cap. Once you’re in the catastrophic phase, Medicare covers your drugs at $0. No discount program can beat free.
- Insulin. Medicare caps insulin at $35/month regardless of list price. No discount program can match this for most insulin brands.
Quick decision guide at the pharmacy counter
Is your current Part D plan giving you the best coverage?
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Get My Free Drug Plan Analysis →Frequently Asked Questions
Can I use GoodRx with Medicare?
You can use GoodRx, but not for the same prescription at the same time as Medicare Part D. If you use GoodRx for a Part D-covered drug, that purchase does not count toward your deductible or $2,000 out-of-pocket cap. For drugs not covered by your Part D plan, GoodRx is a solid option.
What is Mark Cuban’s Cost Plus Drugs?
Cost Plus Drugs is a cash-pay online pharmacy that sells generic drugs at the manufacturer’s cost plus 15% markup plus a $3 dispensing fee. It operates outside the traditional pharmacy benefit system and cannot be used with Medicare. It is strongest for generic drugs not covered by Medicare or where Medicare copays are high.
When should I use GoodRx instead of Medicare?
GoodRx may be better when your drug is not on your formulary, when your plan placed a generic on a high tier, or when you take inexpensive medications and won’t come close to the $2,000 out-of-pocket cap. For brand-name drugs and specialty medications, Medicare is almost always cheaper.
Does using GoodRx affect my Medicare coverage?
Using GoodRx for a drug covered by your Part D plan means that purchase doesn’t count toward your deductible or cap. This can be financially harmful if you take expensive medications, as it delays when you reach the $2,000 catastrophic threshold and begin paying $0.
Is Cost Plus Drugs safe and legitimate?
Yes. Cost Plus Drugs is a licensed pharmacy operating under the name Mark Cuban Cost Plus Drug Company. It is a legitimate, NABP-accredited pharmacy that dispenses FDA-approved generic medications. It is fully legal and widely regarded as a credible option for cash-pay generic drugs.
